In a sign of the widening investigation into Bo Xilai's family and finances, his older brother resigned from the board of a state-controlled alternative energy company Wednesday.

Bo Xiyong -- who also uses the name Li Xueming -- resigned from China Everbright International "for the best interest of the Company and the shareholders," the company said in a statement. He had been a board member of the Hong Kong-listed company since 2003.

"The Board has been advised by Mr. Li that he ... has decided to resign from the Board and its Executive Committee in order to minimize any possible adverse impact on the Company of certain reports recently published by the media on his family background," the company said. Everbright focuses on wastewater treatment, waste-to-energy projects and alternative energy.

He also is a deputy general manager with China Everbright Group, the state-owned parent company in Beijing, but it is unclear whether he has also resigned from that position.

Media attention has spiraled from Bo Xilai -- the former party chief of Chongqing widely believed in line for a national party leadership role before his March dismissal -- to his family members after his wife, Gu Kailai, was detained on suspicion of having murdered British businessman Neil Heywood in November.

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For a Communist Party official who is supposed to earn a modest salary, there are reports he and immediate relatives are worth tens of millions of dollars through business dealings and powerful political connections.

Professor Ding Xueliang of Hong Kong's University of Science and Technology, who knows some of Bo Xilai's family members, said Bo's former position could have given him unique flexibility to skirt China's tight capital control rules.

"He was not an ordinary member of the Politburo. He was one of the earliest PRC officials who had established wide overseas protection," Ding said. "That gave him enormous advantage to accumulate wealth. Once you've established overseas companies outside of China, it's very easy to shift money around."

Bo gained national prominence when he moved in to Chongqing in 2007 and began his "strike black" crackdown on corruption and gangster activities. The campaign implicated millionaires, local officials, police officers and gangsters involved in bribery, prostitution, gambling, drugs and guns.

Since his dismissal, allegations have come to light that suggest the crackdown was as ruthless as the criminals targeted.

"A Chongqing business man told me once 'This is not a legitimate government that hates the mafia. This local government acts like a big mafia boss that hates the small mafia'," Ding said.